Paleontological data have for long been paramount in providing a long-term perspective on global biodiversity. But all is not as simple and secure as it once seemed. Apparently rapid diversification events recorded in the fossil record have been challenged by new molecular data (Bromham et al. 1999; Wray 2001; reviewed in Smith and Peterson 2002), certain mass extinctions are not as well founded as was previously supposed (Smith et al. 2001; Peters and Foote 2002b), and even such a deeply cherished belief as the long-term trend of increasing diversity through the Phanerozoic is once again under question (Alroy et al. 2001; Peters and Foote 2002a). Why is the fossil record not currently providing us with reliable, clear-cut data, and what can be done to correct the situation?

THE ROOT OF THE PROBLEM

Unlike the biological fraternity, paleontologists have concentrated not on estimating absolute numbers of species that may have existed, but on using time-series data to say something relative about global diversity dynamics. Taxic counts at generic or family level have been used as a proxy for species diversity, and rises or falls that occur between time intervals then used as evidence for changing global diversity. This, however, throws up a major complication: Time-series analysis requires that the biota from each interval be uniformly sampled, or, if not uniformly sampled, that biases in sampling at least be understood so that any differences can be factored out. But this complication until recently has been ignored—at best preservation and sampling biases have simply been assumed to be random over time (Sepkoski and Raup 1986 …